The present invention relates to a force and torque sensing element, and in particular to a device for measuring forces and torque in different directions. The device includes a rigid, round hub, and an annular flange that is disposed parallel to the hub. The flange and hub are connected to one another via four spokes that are arranged in the shape of a cross. The spokes are secured in the hub, and are deformed by a load due to their dimensions. Such a deformation is measured with the aid of elongation-measuring strips, with the hub and flange themselves remaining rigid.
Known sensing elements (sensors) of this general type measure the force between two connection or mounting flanges in three directions, which are at right angles to one another, independent of the point of application; the same applies to the torque (a total of six components). Many of these sensors operate on the basis of elongation-measuring strips, in connection with which it has been shown to be expedient to connect the mounting flanges by easily deformable rods, the deflection or bending of which was measured (see, for example, German Offenlegungsschrift No. 32 13 319 A1), permitting conclusions to be made with regard to the load forces and moments.
In a manner similar to that of the aforementioned German Offenlegungsschrift No. 32 13 319 A1, the inventive sensor comprises a central hub N (see FIGS. 4a and 4b) and an outer, annular flange F, with the hub and flange being interconnected by four spokes, 1, 3, 5, and 7 that are secured to the hub. Fixed to all four sides of each spoke, as close as possible to the location of securement of the latter, are elongation-measuring strips, for example 1a, 1b, 2a, 2b, etc. (see FIGS. 4a and 4b). Deflections of the spokes not only in the plane of the flange, but also in a plane disposed at right angles thereto, can be measured by these elongation-measuring strips.
As can be seen from FIG. 10 of the aforementioned German Offenlegungsschrift No. 32 13 319 A1, the spoke ends are secured to thin plate-like strips (designated cords 19, 20, 21, 22), so that when a force occurs, for example in the X-direction, the spokes 11, 12 can be easily displaced in the X-direction, i.e. at right angles to the plane of the cords 19 and 20. The spokes 13 and 14 are held securely in place in the direction of the tangents of the cords 21 and 22, so that these spokes bend or twist, whereby the tangential force in the X-direction can be measured. However, when an external torque occurs, for example in the X-direction, this arrangement does not preclude operation in the transverse direction, i.e. at right angles to the plane of the drawing of FIG. 10, since the cords 21, 22 actually prevent tangential displacements in the longitudinal direction of the cords. This shortcoming is remedied in the arrangement shown in FIG. 3 of the aforementioned Offenlegungsschrift via an additional support member that is disposed at right angles to the cords; however, this leads to an expensive construction.
It is an object of the present invention to provide an effective device of the aforementioned general type that eliminates the drawbacks of the known arrangements, while being economical to produce.